1. Field of the Invention
The present invention relates to a control apparatus for use with an image blur prevention apparatus that prevents an image blur from taking place due to a vibration of an optical apparatus such as a camera, a video camera, or the like.
2. Related Background Art
Various image blur prevention apparatuses used for cameras have been proposed. As an example of such apparatuses, a related art reference disclosed as U.S. application Ser. No. 07/701,051, filed May 16, 1991, which was abandoned in lieu of application Ser. No. 08/117,346, filed Sep. 7, 1993, which was abandoned in lieu of application Ser. No. 08/313,398, filed Sep. 27, 1994, which issued as U.S. Pat. No. 5,479,236 on Dec. 26, 1995, is known. In this apparatus, an image blur correction optical mechanism is incorporated into a zoom lens or the like. A drive amount coefficient of the image blur correction optical mechanism corresponding to a zooming operation, namely a variation of image blur prevention sensitivity, is corrected so as to correct an image blur. Thus, a good image blur correction effect is obtained in the entire zoom range. The correction of the variation of the image blur prevention sensitivity is performed in the following two ways.
(A) The positions of a zoom lens and focus lens are read as analog data. The image blur prevention sensitivity is calculated corresponding to the analog data being read. The drive amount of the image blur correction optical apparatus is corrected corresponding to the calculated image blur prevention sensitivity.
(B) The moving ranges of a zoom lens and a focus lens are divided into respective predetermined regions. The value of the image blur prevention sensitivity corresponding to each region is stored in a ROM of a microcomputer. Values stored in the ROM are read from a so-called lookup table. The drive amount of the image blur correction optical mechanism is corrected corresponding to the value being read.
However, such two correction methods have the following problems.
In the method (A), where the image blur prevention sensitivity is calculated with analog values, the following problems take place.
1) The calculation function is complicated. Thus, the image blur prevention sensitivity cannot be simply expressed.
2) An analog position detecting apparatus that detects the positions of the zoom lens and the focus lens with high accuracy (non-linearity), high resolution, and high environmental resisting reliability is expensive.
Thus, the method (A) is not practical. Consequently, the method (B), where the lookup table stored in the ROM of the microcomputer is referenced, is conventionally used.
However, in the method (B), the following problems take place. In this method, the accuracy of the image blur almost depends on the number of divided regions of the zoom zone and focus zone. However, as the number of divided regions increases, the following problems take place.
a) The size of zoom/focus zone detectors that are constructed of a gray code pattern and a detecting brush becomes large.
b) The alignment accuracy of the pattern and brush of the detectors should be improved corresponding to the increase of the number of divided regions.
c) Since storage amount of the lookup table increases, an expensive microcomputer is required.
Thus, the number of divided regions cannot be unconditionally increased. Consequently, the upper limit of the number of divided regions in real products is around 16 (4 bits) or 32 (5 bits).
When the number of divided regions of the zoom zone is 16 and the variation ratio (ratio of the maximum value and the minimum value) of the image blur prevention sensitivity by the zooming is 2.0, the error of the image blur prevention sensitivity is 2.sup.1/16 =1.044. Thus, the maximum error amount is 4.4%. This error amount does not remarkably affect the conventional image blur correction. However, when a selected value of the image blur prevention sensitivity table is changed corresponding to the zooming operation and/or the focusing operation, the image blur correction optical mechanism moves slightly, but abruptly. Thus, the image also abruptly moves.
Thus, when the image blur correction apparatus is used for a still camera, if a picture of an object that is being abruptly moved is taken, the picture contains a large image blur.
When the camera is provided with an auto-focus (hereinafter referred to as AF) apparatus, if an image moves while the image is being stored in an AF sensor, the image that is used for measuring the distance between the image and the camera largely blurs, thereby remarkably lowering an image contrast. Thus, the AF accuracy is adversely affected.
In addition, when the image blur correction optical mechanism abruptly moves, an actuator of the mechanism consumes a large amount of electricity. Thus, in addition to this actuator, when another actuator such as a focus drive stepping motor is driven, the stepping motor may not properly work. Moreover, since sufficient electricity is not supplied to the control circuit of the camera, it may malfunction.